The present invention is related to the United States Patent entitled xe2x80x9cMethod And Apparatus For Assigning Frequencies In A Cellular Network,xe2x80x9d Ser. No. 08/850,187, Filed May 2, 1997, by Boyer et al., which is incorporated herein by reference.
This invention relates generally to cellular telecommunications and more particularly to the assignment of channels in a cellular network.
Providers of cellular telecommunication services wish to maintain minimum communication service quality standards when assigning channels to cells. They also wish to distribute and reuse channels as much as possible throughout their networks while maintaining at least the minimum quality standards. Failure to maintain minimum quality standards causes poor quality channels, which leads to customer dissatisfaction. Failure to distribute and reuse channels as much as possible throughout the network leads to increased blockage (i.e., busy signals) for customers and reduced revenues for the service provider.
A service provider""s cellular network is often located adjacent to a neighbor network. The service provider""s network and the neighbor network may share a common spectrum. The use of this common spectrum in one network""s cells located at the border between the two networks has an effect on the other network. For example, at border cells a service provider""s minimum quality standards may not be met due to the way the neighbor network uses the common spectrum. To reduce chaos which might otherwise result at border cells from the completely independent use of the common spectrum by the different networks, the neighbor networks often agree to specified channel assignments at their border cells. In other words, the different networks specify preset identities and locations of channels to be used for the long term in the border cells. As a result of such agreements, the network service providers have less freedom to alter the channel assignments in the border cells because an alteration could adversely affect the neighbor network and be in violation of the agreement. On the other hand, the network service providers have great freedom to assign channels as they see fit throughout the remainder of their own networks.
A channel assignment problem refers to the assignment and reuse of channels in a network""s cells. Network service providers often use computer-based network automated channel assignment tools which, based on a wide variety of information sources, provide solutions to the channel assignment problem for the network. In other words, the automated channel assignment tools provide solutions which assign channels to cells to meet a wide variety of channel assignment constraints. Channel assignment constraints may include, among other factors, the assignment of channels so that minimum quality standards are maintained as thoroughly as possible throughout the network, and the predetermined assignment of certain channels to certain cells, such as cells located at network borders.
However, conventional automated channel assignment tools fail to adequately account for service quality degradation which may result from border cell agreements. A conventional automated channel assignment tool does not assign a channel to a cell if that assignment would cause service to degrade below the minimum quality standard at a remote cell. However, service quality may already be below the minimum quality standard at the remote cell as a result of a border cell agreement. Due to this pre-existing substandard quality, the conventional automated channel assignment tool resists assigning the channel for distances which are much greater than a typical reuse distance. In one example, the conventional automated channel assignment tool resists assigning the channel for a maximum propagation distance away from a border cell where the degraded service has been detected. The maximum propagation distance is a function of the curvature of the earth and is much greater than a typical reuse distance. Consequently, fewer channels are distributed throughout the network than desired, and customers are more likely to experience blockages.
What is needed therefore is an improved apparatus and method for an automated channel assignment tool which adequately accounts for the service quality degradation which may result from border cell agreements.
Accordingly, it is an advantage of the present invention that an improved method and computerized apparatus for assigning cellular channels to locked and unlocked cells are provided.
Another advantage is that an automated channel assignment tool which adequately accounts for the service quality degradation which may result from border cell agreements is provided.
Another advantage is that channels are assigned to interior cells of a network so long as such assignments make no more than an insignificant deterioration in service quality at border cells which experience degraded service quality due to a prearranged assignment.
Another advantage is that, except for cells which are subject to prearranged channel assignments, channels are assigned to cells so that no cell experiences less than a minimum service quality.
The above and other advantages of the present invention are carried out in one form by a method for assigning channels in a cellular network to locked cells having prearranged channel assignments and to unlocked cells having channel assignments that are not prearranged. The method calls for allotting channels to the locked cells in accordance with a prearranged assignment plan to effect assignment of the channels in the locked cells. First interference statistics are calculated to characterize interference at the locked cells for the channels. An allotment of a first one of the channels to a first one of the unlocked cells is simulated. Second interference statistics are then calculated to characterize interference at the locked cells for the first channel in response to the simulation. The first channel is allotted to the first unlocked cell to effect an assignment of the first channel in the first unlocked cell if the second interference statistics indicate less interference for the first channel than is indicated by the first interference statistics for the first channel.